Question

Refer to the Scheer Industries example in Section 8.2. Use 6.85 days as a planning value for the population standard deviation. a. Assuming 95% confidence, what sample size would be required to obtain a margin of error of 1.5 days (round up to the next whole number)? b. Assuming 90% confidence, what sample size would be required to obtain a margin of error of 2.5 days (round up to the next whole number)?

Answer 1

a)

for 95 % CI value of z=	1.960
standard deviation σ=	6.85
margin of error E =	1.5
required sample size n=(zσ/E)2                                         =	81.0

b)

for 95 % CI value of z=	1.960
standard deviation σ=	6.85
margin of error E =	2.5
required sample size n=(zσ/E)2                                         =	29.0